Should I be worried about a squealing sound coming from my sony receiver at high volume of b-only signal?

using a sony str-d915 to drive dual subwoofers using the LFE from my pioneer THX receiver, i can hear a clear squealing noise from the sony reciever when I run a heavy-b song... could this be a danger sign that I am running at improper resistance???? I don't want to break anything, but I don't have the tools right now to check the sub resistance, as they are car subs and could be in series or parallel.