growling noise coming from rear when under load
 

I have an '07 Suburban 1500 with ~180k miles on it. The rear is making a growling noise when under load. If I take my foot off the gas the noise goes away for the most part.
I changed the oil to see if that would make a difference but I don't think there was much change.
Everything looked good though. No metal parts.

I've read that it can be a number of things but I haven't seen anyone write back as to what the problem actually was.

I toe a lot and want to get this fixed before next month.

Any suggestions?

Thanks.