I've got an '88 XJS V12, and lately I've had a number of unusual noises coming from the transmission tunnel. I notice it immediately upon startup, in park and neutral, and in reverse and forward gears over about 1,500 rpm. The trouble started after getting stuck in the snow, developing a flat, and having to get a tow out.

I only hear and feel the vibration while inside the car, and I'm not noticing any reduction in power or other unusual behavior. Also, the transmission mount has recently been replaced. That took care of a clunk, but the grinding/rumbling noise is still present.

My car's with the mechanic right now, and they've confirmed that the transmission itself is in good condition, but they still can't pinpoint the cause of the noise and nor could I with my admittedly limited inspection.

I'm curious as to whether this has happened to anyone else, and if so, what the culprit was. I got a potential lead in another thread, but didn't want to hijack it further.

 

The gearbox mount is supported on two separate pieces if welded bracket, both of which bolt to the car. The propshaft or UK at the gearbox end is fouling on one of these. most likely this one:

which is revealed once the first Y shaped plate is removed. The fouling could be because of a collapsed spring in the mount, or just some fixing bolts come loose.

 

First thing I'd check would be that the exhaust systems aren't touching anything anywhere. They take a tortuous route over the rear suspension and it's very easy to contact the body, suspension, whatever.

 

+1 on the rear mount. Thoroughly check all the components to ensure the locating pin and cotton reel are not allowing metal to metal contact.
If possible try to move the g/box up and down listening for contact at the rear mount.

 

Yep,

Stuck in snow, so forward, back, forward etc trying to get out, didnt work, so tow needed.

Trans mount #1, exhaust #2, LH engine mount #3.

Time to get under the beast and look around.

 

Thanks for your help, everyone, but this mystery as of this time remains unsolved. The motor mounts are good, the transmission mount was replaced, and the exhaust system is in good shape with no signs that it's making contact anywhere. I certainly didn't see anything out of the ordinary, and neither did my mechanic, so I'll be getting another opinion soon.

 

Did the guys actually remove the two brackets that hold the gearbox mount? Unless this is done you cannot actually see if the prop is fouling the bracket in the diagram I posted.

 

I have just twigged your point that the noise is there in neutral and park, when the prop is not rotating. This HAS to be a gearbox or TC fault. How far was it towed?