97 suburban 3/4ton 454/ ticking sound appears to be coming from muffler

[Load619]

Recently changed my plugs and wires, after I get everything hooked back up, I started the engine, and put it in reverse, as I start to back up, I hear a ticking type sound, it sounds as if it may be coming from the muffler, I'm not sure what the problem is, any help would be greatly appreciated...