Balancer belt whine...

The whine is really quite loud, annoying when driving. It completely disappears when I run without the balancer belt, so its not the timing belt...

Everything has been replaced: belt, tensioner and idler. The belt is already really loose: I can easily twist it 150deg or so and it's already flapping around a bit. I don't feel comfortable loosening it up even further. The tensioner is tensioned clockwise, as required, and the idler is just touching the upper span of the belt, as required.

Any ideas on what can I do to make the whine quieter?

Cheers!