I installed my Q150 last night and am VERY happy. This evening my girlfriend kept looking out of the window and complained of "a car running outside". She said that she heard this last night too. We finally pinpointed the source of the noise.. It was the sub.. Its constantly generating a low frequency hum. Its not very loud, but very noticable.. But as its a VERY low frequency, its hard to hear.. But once you switch the sub off, you know it was there.. Even with teh cables remove (except the mains) it still does it and the controls has no effect. I really hope that my unit is fault and I can get it replaced.. But if its a general problem, there is no way that I can live with it. Its not like I can switch if off when its not in use as its located behind the TV and totally unaccessable. Can any other Q150 users confirm that they DONT get this. I am not happy now!!!!!