I have a "Ruud Achiever 90+" high-efficiency furnace installed in my home. This Ruud unit seems like a great product with good build quality, engineering, etc., except that the PVC pipes that vent it to and from the outside make a lot of noise whenever the burner is firing. It's a high-pitched, multi-frequency whine reminiscent of the transporter noise from Star Trek TOS. Anybody else ever deal with this? Are there mufflers or something else available? This noise keeps me up at night, and since the pipe exhaust pipe is aimed at my next door neighbors' bedrooms, they undoubtedly hear it, and would appreciate if it was quieter, too. What's the best way to quiet this thing down?