Why has my car's engine started making this sound?

[mshan]

1999 Audi A4 1.8 Turbo Quattro manual with almost 53000 miles on it.

Today I noticed that when rpms hit about 2000 rpm engine starts making this funny noise (starts and stops before actual engine revving noise) and goes away at 2600 rpm.

Idle now almost sounds like a diesel engine.

So far, car seems to drive normally.

What's going on?

 

[jagec]

What kind of "funny noise" exactly? Like a ticking/pinging? Does it occur more under load (heavy acceleration, hills)? Does it occur under engine braking?

From what you've described, it could be knocking. This may or may not be a major problem, depending on the cause. When's the last time you had a tune-up? New spark plugs/wires? You HAVE been using premium fuel every time, right? Maybe it's been "knocking" the whole time, but now the knock sensor is malfunctioning. Maybe there's a crack in the exhaust manifold. Maybe there are lots of carbon deposits (do you ever flog on it? If you drive like a granny ALL the time, sometimes problems crop up.) Maybe the spark plugs are the incorrect heat range.

More info is needed.

 

[mshan]

It's kind of a short burst of high frequency revving that precedes actual engine revving. Starts at 2000, ends at 2600, both when rpms are going up or when rpms are going down. Idle noise now sounds like a diesel engine, though car seems to feel like it is driving normally.

On another forum, someone mentioned possibility of "Misfire at idle, bad turbo vacuum leak, exhaust leak. any of those, or all of them... that gen audi is known for bad turbos"

Kinda of getting worried about a bad turbo.

Do you think it is safe to drive around town till I get the problem evaluated and fixed.

Also, a couple people have mentioned change the oil. Do you know reason they say this?

 

[thedarkwolf]

Hard to do the sounds things over the net. A bad lifter will tick like crazy and usually more noticeable at idle. My miata sounds like a diesel when you first fire it up after setting awhile until the lifters pump up again which takes a couple mins. As long as the ticking goes away its not a big deal but if it keeps doing it after the engine warms up then you need to do something about it. The oil thing if its just a lifter is because the little holes were the lifters get their oil can fill up with goo and changing the oil can clean them out and stop the ticking.

 

[mshan]

Thinks it safe (won't damage engine) to drive my car around town till I can find a mechanic to evaluate it?

 

[ElFenix]

high frequency sounds are usually the turbo spooling up on that engine

 

[mshan]

Not really high pitched sound, just higher frequency than engine revving up (starts and stops before engine revs too).

If it is a defective or faulty turbo, is it safe to do some day to day driving till I get it fixed?

I've been googling lifter tick and engine idle isn't quite that ticky sounding. Still may try an oil change and see if problem goes away.

 

[sniperruff]

my friend's car had an exhaust leak and it sounded like a diesel. might want to check that out.

 

[mshan]

Idle sounds sort of like a diesel engine now (i.e. not exactly like a diesel engine, just sort of like one, though ticking is not so pronounced).

Main issue seems to be that rev dependent noise. I think my turbo kicks in at 1800 rpm, but not sure where it tops out (doubt it is 2600 rpm, though).

What do you guys make of the fact that rev dependent noise totally disappears above 2600 rpm (and occurs going up and decelerating down into that range)?

 

[Demon-Xanth]

Check the exhaust leading to the turbo. You likely have a leak or a hose that has come off.

 

[mshan]

"Check the exhaust leading to the turbo. You likely have a leak or a hose that has come off."

I am going to take it to a mechanic, but can I safely (i.e. not risk damaging the engine) drive around town till I do so.

And how costly should this repair be?

 

[mshan]

Started car this morning (oil levels appear fine) and idle noise is best described as dull plastic rattling noise that seems to be coming from deep within the engine itself.

I think it is always there, but in car, I think it's the same sound I hear from 2000 rpm to 2600 rpm.

Any ideas of what's going on?

 

[mshan]

I was listening to my engine at idle and during driving and came to the conclusion that it sounded like a dull plastic rattling (or even dull aluminium) that was producing an "rrrrrr" sound between 2000 and 2600 rpm.

Trying to localize further seemed to be coming from bottom of engine, so I took a look under car and it looks like that piece of plastic that protects bottom of engine compartment is loose.

All screws look like they have fallen out and there is like one screw remaining on front driver's side rear part of casing.

I am going to get my oil changed anyways, but do I have to go to the Audi dealer so they can replace those screws, or can any shop that does oil changes do the same?

Hopefully once that's fixed all sounds will go away and that was my only problem.

 

[jagec]

Any shop that does oil changed *should* be able to replace the screws, but the question is how much effort they'll put into finding the right size, or if they'll just force something to fit.

Take off the remaining screw, count how many you'll need total, and then go to a hardware store and buy replacements with the right size and threading.

I'm guessing that this will cure the problem. That's harmonics for you.

 

[mshan]

Found two screws still there, so I retightened them.

Audiworld Forums said there are supposed to be 6 screws and 2 plastic ones.

After tightening those two, engine really sounds like a diesel engine now. Seems like something else is going on.

I'm hoping its something that oil change can fix (people have mentioned clogged hydraulic lifter?), and not something involved and expensive (turbo, though car seems to drive totally normally despite noise).