i've just bought a 96 850 t5 it has done 50000 with a full dealer history, i changed the oil and filter this weekend (used a volvo filter and gtx magnetec 10/40 oil) because the oil didn't look very clean.

the day after doing the change i went for a 1 hour run, when i was pulling up on the driveway i noticed a rattle noise coming from the engine area its very faint and only happens when the engine is reved to about 1500rpm or more

ie. if i rev it to 1500 rpm it will rattle at 1500rpm and then nothing as the revs fall back to idle or if i hold the revs at 1500rpm it will make a rattling sound itermittently as long as i hold the revs at 1500rpm.

the oil is at the max mark and there are no leaks also the engine is quite when starting from cold and at idle (hot or cold). is the engine f***ed??? a friend said its the fan belt, could he be correct??? could it be the fan/timing belt idlers/tensioners ratlling???

any help would be helpful thanks very much.