Rattle at about 1750 RPM in 1990 740 Turbo

Have just bought a 1990 740 Turbo, and noticed a rattle in all gears
(4 sp w/OD) at around 1750 RPM. It sounds like a "loose tin" kind of
rattle, almost like a loose clamp on muffler or something. It's
difficult to locate, bc only happens when driving. Any ideas? The
car is otherwise A-1, running very well in all respects. TIA.

skid

 

Check the heat shield above the tail pipe.

 

Also check first exhaust box if car has catalyser fitted as they often fall
apart after several years.

All the best, Peter.

700/900/90 Register Keeper,
Volvo Owners Club (UK).

 

Heat shield a very common thing about the 740 all years
Regards
Nightmare

 

Heat shield is as others said a likely candidate. Also there is a very
long metal "hose" that routes warm air to the intake that if not
secured makes buzzy rattly noises. Also, a failing catalytic converter
will rattle. Finally, check the entire exhaust system for integrity.

 

Thanks for all the input - I can't find anything particularly loose in
there - so I'm contemplating taking it in (thankfully I have someone I
can trust!), but just wondering why it might only happen at 1750
RPMs...that's a curious one for me. TIA.

skid

 

If the engineer in the family was writing this she would probaly start
babbling on about harmonics and such stuff. Look at that heat shield
first. A decent repair shop will have a set of remote microphones that
they can position around the car and selectively listen as the car is
driven.