This is really annoying me, I can't work out what's going on. Car is a 4th gen Mustang with a 3.8 V6 and 4 speed 4R70W automatic transmission.
For the last few weeks I've been noticing a 'rumble' every now and then. At first I thought it was only in 3rd gear so just drove to keep it out of 3rd as much as possible, but I've now realised it occurs in neutral and other gears.
So, what do I know?
- It's low frequency, probably 1-2 cycles per second. Intensity is variable and I think it's related to power, rather than engine speed. It's much more noticeable at 1,500rpm when driving (which is why it often appeared when I was in 3rd), and I can't feel it well enough at other speeds to be sure whether it's the amplitude or frequency (or both) that's changing
- Testing it in neutral/park/held on the brakes: it's not noticeable at idle. About 1400 RPM it starts, intensifies at 1500, drops off a bit, peaks at 2000, then rapidly becomes unnoticeable
- It doesn't seem to occur when cold. It's hard to be certain due to the roads around here, but in neutral it doesn't occur at all from a cold start. After 20 minutes driving it's definitely there
- It doesn't seem to be affected by air con, and the harmonic balancer visually looks OK
- Transmission fluid is at the right level, pink and doesn't smell burned. The fact it occurs in neutral rules out anything behind the torque converter, and I haven't noticed any other torque converter issues
Any great ideas? I suppose it might be an engine mount, but they're buried under a lot of engine so I've not got at them yet