Annoying helicopter reverberation sound resolved
Tracked down a strange noise in my 95 LX 4.6. Searched the site for possible solution, but couldn't find that this had been covered before.
After putting everything back together following an EGR tube cleaning and EGR valve replacement I was hearing an annoying pulsating sound at low load with engine around 1400 RPM and when decelerating to a stop. Sounded like an exhaust leak but I could only hear it while driving, couldn't hear it from outside the car or under the hood.
Ran it while on jack stands looking for a leak, and I thought I could feel some air around the left side exhaust manifold flange. Redid the studs and nuts on that side and torqued to spec. No change.
Took the exhaust pipe off at the resonator, ran the car and held my hand over the resonator outlet: couldn't hear any leaks.
Redid under the hood, took everything off down to the throttle body adapter ("elbow"). Made sure the bolts on the EGR valve and nuts on the EGR tube were tight. Made sure the air intake and throttle body were clear. Tried it again. No change.
Thought maybe the helicopter sound was because I put in new oil after running Bardahl stop leak and now the engine needs Bardahl to keep from knocking. Added Bardahl, no change.
Well, while I was doing the EGR tube job and while the exhaust was down, I replaced the rear engine support insulator (motor mount). No reason other than I had it on hand and was going to do it after replacing the motor mounts. So now I swapped back to the original transmission mount and the helicopter sound is gone.
Transmission mount was Westar EM2707 from Rockauto. I checked the transmission mount before swapping it back, all the bolts were tight. The Westar unit doesn't any obvious defects that I can see, but for some reason my car did not like it. Makes me wonder about the Westar motor mounts I bought and was planning on installing some time this summer.