A buzzing rattle

I have noted that when accelerating in a normal fashion that when the RPM gets up around 4200, then engine sets up a kind of harmonic buzzing rattle, like something is seriously loose. If I close throttle, the noise goes away, but if I continue to push the revs higher, the rattle continues until I upshift, then it will be OK until 4200 RPM again, up through third gear. Is this normal? It doesn't seem to do it in fifth, though by then the bike is doing 80MPH.

I have noted that when accelerating in a normal fashion that when the RPM gets up around 4200, then engine sets up a kind of harmonic buzzing rattle, like something is seriously loose. If I close throttle, the noise goes away, but if I continue to push the revs higher, the rattle continues until I upshift, then it will be OK until 4200 RPM again, up through third gear. Is this normal? It doesn't seem to do it in fifth, though by then the bike is doing 80MPH.

Evening SoCalBmr

Well, it's partially normal. In the 4000-5000 RPM range the engine goes into a buzz mode & that is normal but the harmonic buzzing rattle might or might not be normal.

The problem is, once the engine enters it's buzz range then anything that is loose, or hanging on a lever can light off & start buzzing.

You might want to check the alternator for being tight, check the engine & frame bolts for being tight, check the exhaust system for ground outs & anything loose or touching, check shift linkage & short arm for being loose, check steering bearing for being loose, etc. It could even be the clutch parts buzzing.

You can rap on things with a soft leather mallet or rubber mallet to see if they are loose or are capable of buzzing.

My bike had a similar problem. It turned out to be the add-on sidestand foot. Like DR said, it could be almost anything.

Ironically enough...I have the same exact sound on my 2004 RT at the 4200 range. Being new to the BMW world (V-Twin guy) I assumed it was normal. I was use to hearing all sorts of noises on my Ultra Limited, especially on hot days.

I don't remember the RPM it happened at, but I've chased similar symptoms before. As dirtrider mentioned, the exhaust can be the cause. Two specific points in the exhaust which I've run into are the lower mounts to the center stand brackets (if your bike has them) and the rubber hanger bushing at the rear. BMW stopped using the lower mounts so if those are the culprit, just remove them. Also check the rubber up-stop for the center stand.

Well, now I have something to look over. That noise is annoying!

Or just wear earplugs.

Next time you have the gas tank off check the engine mount connections for loose hardware.

Last year when I was working on my 03 with about 120k on the clock, I noticed fretting on one of the upper mounts (fine rust powder).

It turned out that this bolt/nut was loose.