Intermittent vibration through car (3.8 FHC)

[david muir]

Was out for pre-MOT run the other day (car hasn't been used for a good few months) and 'detected' a strange , disturbing vibration through car!. Stopped car and turned round for home -no vibration. Turned again and after a couple of miles, vibration returned. Stopped etc etc. Then vibration disappeared and was able to get up to a good speed .
I don't want it to be the propshaft U/Js but I think if it was them , it would be vibrating all the time.(have had this 15 years ago). 2nd thought was flats in tyres after sitting (Dunlop R5 Racing)-had this before as well.
It's the intermittency that's disturbing!
Any other ideas folks??
Thanks
3.8 E FHC

[christopher storey]

Could well be flatting of the tyres, which will gradually disappear as the tyres warm up . Intermittent nature is a bit puzzling, but it so often happens - I have had it with wheel balance, which defies logic. It could also be solid grease in the prop u/js and /or the drive shaft u/js, which gradually becomes more fluid

[chrisfell]

It's a Gremlin. Some say that these are imaginary creatures, others that the noises we hear as we drive our cars listening for things that are wrong are mostly in our heads. I'm convinced Gremlins are responsible. Real problems are always more obvious, or develop from something a Gremlin has started.

Make a note of the circumstances, speed gear road surface etc. Then see if the same vibration occurs in another car at the same speed at the same place.

[Hugo]

If I had to hazard a guess I'd say propshaft. These can be intermittent, appearing at some speeds and not others, and under some load conditions and not others. I would try reversing the load when it occurs (i.e. take your foot off the throttle) and just play around to see what aggravates it and what makes it go away. If it is a propshaft it will only get worse, which if nothing else will make it easier to identify.
Or you could be really unlucky and have a flange nut come loose. (centre nut).