Terrible clattering noise in the under side of engine compar

My 1995 Chevy Blazer has 150,500 miles. I have recently had the front and rear drive shafts, joints, and bearings replaced. A couple of days ago it started making a knocking noise which has progressively turned into a loud clattering noise. It almost sounds like it's shaking something loose. I was told that it sounds like a rod or rocker arm, but I'm not so sure. But you see the problem is I'm a single woman and I guess they think I don't know anything about this stuff. My oil pressure has not changed any at all, the noise is worse when just sitting still (as soon as I give it gas I don't hear it), I seem to be leaking fluid from the rear trans seal (or in that area). The engine preformance has not changed as the noise is getting worse. Any suggestions on what I can do or what it might be. I'm getting tired of mechanics sticking it to me because I'm a lady. I just recently had it in the shop also for what they told me was a fuel rail problem when it could've been taken care of by fuel filters. Thank you so much for any help you can give me.