Thank you all!

Empire_2

Did you get what I was talking about with the louvers on a return grill that would,....Harmonically pitch and drive me crazy? I thought that is what you had, but I guess not. Glad you found that annoying sound. Kinda drives Ya crazy...

See Ya

Mike T.

Constantin

The source of the organ pipe has been found...

... covering myself in the process with Duct Butter, Pookie, or whatever the mastic is called in the trade was worth it.

The most likely culprit: a 1/10" wide slit at the back of the air handler where the intake side meets the duct work. Once that seam was closed, silence reigned. The fan can now modulate up and down, w/nary a noise. Brilliant!

As to why the Air Handler was not sealed against the ductwork, that is a different question and probably impolite to inquire about.

Also of interest, watching the 4 ton air handler making the ductwork do the rhumba at full speed. Wobble, wobble, wobble, the ductwork goes as the sheet metal oilcans despite the obligatory "X" breaks to reinforce/stiffen it.

Checking on the return registers, there is some serious air velocity when the air handler is running at full tilt. My uneducated guess is a lack of return duct capacity, but given that the conditions under which all 4 zones will be calling will be remote to none, it's not something I will loose sleep about.

So thanks again for the tips, I greatly appreciated them.

Eugene Silberstein 3

Glad...

Glad to hear (or not hear) that the situation has been remedied.