I know what a ooga horn sounds like but my GMMP never sounds like that.
On cold start up you get that huge sucking noise. Then driving you get the turbo spool noises with whines and whistles. The BOV releasing boost sounds more drawn out rather then the usual pop. You get some strange noises with partial boost/vacuum. You also get the "three stooges sound" when the compressor wheel surges when the BOV doesn't release boost quick enough.
Most of the strange noises come from having an undersized BOV on the compressor housing.
Hahn's BOV looks good, check out that thread:
Billet Blow-Off Valve System for GXP & RL
