Radio frequency interference in speaker when using GSM for call.
 

When my phone is set to GSM, there is a lot of noise in the speaker.

The same noise you get on your radio if you put your phone to close to it during a call.

Is this a common problem?

Re: Radio frequency interference in speaker when using GSM for call.
 

Yes I experience the same.

Re: Radio frequency interference in speaker when using GSM for call.
 

If it's the N900 speaker, it's a hardware fault, likely some grounding went MIA. Return, most likely.