my 1990 superextra td has developed a noise/vibration at around 900rpm.if you are in drive(auto)and touch accelerator to pick revs up to 900rpm the vehicle developes this resonance quite noticeable from drivers seat,above this rev range and unable to hear.could it be an overtight belt somewhere? - (#2287) Glynn Smith, 20 Feb 02

Glynn
Needle in a haystack time. You need to locate the source of the vibration before diagnosing the fault. Lift the engine compartment cover and while a helper presses the accelerator, try and locate the fault. Is it engine (place a block of wood against block and ear to other end), is it ancillaries, maybe even not connected with engine at all.
Ian - (#2305) Ian Dunse, 21 Feb 02

When you said "quite noticeable from drivers seat" I recalled Patrick Adams posting 22 Jul 01
"I have had a knocking sound, which I thought was coming from under my seat". It maddeningly turned out to be the roof aerial. See Ace Answers - Faults - Noise - "Knocking. What's that knocking?" - (#2308) Dave Mason, 21 Feb 02

I had a similar symptom of noise but at a bit higher revs. The noise disappeared when I next changed the oil for some reason! (oil wasn't particularly overdue for changing). Maybe just the passenger seat was not quite fitted down.
Jim - (#2309) Jim Snowden, 21 Feb 02

Me-thinks!
Similar to my early noises which was diagnosed as a loose crankshaft pulley. Several of which have been reported on this site. Get a socket / spanner on your pulley bolt and check if it turns ( the bolt that is not the pulley ). Also feel for a crankshaft pulley and / or washer that has movement. - (#2314) stephen judge, 21 Feb 02