M3 E46 - Low RPM engine rattle - Any ideas?

[m3604]

Year: 2001 M3 E46 (Stock)
48,000kms
6spd Manual Transmission
Oil change done every 6000kms
Use 91 Octane fuel

I am experiencing some engine rattle noise at low RPMs. The sound is like metal vibration or tapping noise and it sounds like something is loose when accelerating.

I've noticed when driving at a constant speed with the RPMs around 2000 in any of the gears for example in 3rd or 4th gear around 50 -60 km/hour and you apply the gas quickly there is a metal rattle noise until you reach 3000 RPM or more.

The sound is not apparent if the revs are higher than 3000 RPM and applying the gas quickly and shifting at a higher RPM range.

The sound is minimal if the gas is applied slowly from 2000 RPM and allowing the RPM to climb slowly.

The M3’s are a higher revving engine but with acceleration at cruising speeds and low RPMS shouldn’t make such a noise? Should it?

I’ve had it checked out briefly during an oil change and the mechanic did not notice anything loose. He said it is common with vehicles in general having the engine noise because too much fuel is being applied so the engine is lagging or choking if in a higher gear and low speeds.

Any ideas or suggestions would be great.

Thanks,