I can achieve normal transmission when while media player is playing something I press and hold the down arrow on the hardware keyboard. The active application may be different. The calculator for example.

If no key is pressed there is no carrier frequency. Noise only from the receiver.

Did a little testing to see what happens when the key is pressed.

Nothing releted chaged in the /sys/class/i2c-adapter/ tree when the key was pressed and released later.

Verified by dumping file's content this way:
root@Nokia-N900-42-11:/sys/class/i2c-adapter# for i in `seq 1 1000`; do find . -type f | while read f; do echo -n "$f: "; cat $f 2>/dev/null; done > ~/radio-test/res$i; echo $i; done

No related changes found in diffs between files.