740 Strange noise at 3000 rpm

Hello all.
Its a n/a 2.0 740.
I have this rattling/grinding noise for a while (more than a year), here is a video from the interior and from outside. It happens only at 3000 rpm, no more no less, when driving or standing, hot or cold, in gear or in neutral (its an automatic) so I believe its not from the transmission.
The car works great, not loosing oil or coolant and the fuel economy is fine for this model. Its just that annoying noise.
I checked the exhaust pipes all under the car and they're not loose, removed the heat shield from the exhaust manifold but no results.
Any clues?

thanks!

Maybe a loose or worn timing belt tensioner? They can make noise for awhile before they finally fail. Check for an alternator that has a fan scraping because of worn bearings. That may be the rpms that the bearing play makes the alternator fan hit. Just some possibilities that come to mind.

Thanks! |
My alternator don't have a fan.
How can I check if its the timing tensioner? Try to move it by hand? look if its shaking when the car is running?

There is a cooling fan on the front of all these volvo alternators. It is either external like a bosch one or internal like a Denso alternator.

The timing belt tensioner is under the plastic over on the front of the engine. Inside with the timing belt. It is located where there is a rubber plug covering a hole on the front of the cover. You can try to retorque the nut under the plug. Loosen one full turn then retorque to 37lbft. Usually a 15mm nut on the B200 type engine.

If the sound changes it may be time to replace the tensioner and belt. Could also be something simple like the plastic fan hitting the shroud. Look around in there and get comfortable knowing the engine. There is plastic like the timing belt cover that the fan belt can rub on. Stuff like that.

Thanks, you were right.
Yesterday I opened the top timing cover to see whats going on in there. The belt was all cracked. Took it to a shop, they replaced the whole thing (belt, tensioner and seals).
Now its smooth and quiet.
The guy there said that this engine is an interference engine because the pistons have flat tops, an that I was lucky to inspect that in time. I think he is wrong, is he? engine code is B200F.

Thanks for letting us know. Glad you got it sorted out. I guess it depends what cam is in there. Also I think the interference factory engine is the B200K with the carburator. Your's is fuel injected if it is an F engine. I know the B230F is non interference.