I just bought some silencers from our local and only sporting good shop.  They only had one kind, Tarantulas.  I put them on a Martin Howatt Hunter 65#@28".  The top one desintegrated very rapidly (30 shots), while the bottom one still looks like new.  

I thought maybe the top had come out of a bad run of material, but they were from the same piece of material and I had to cut it in half.  

Has anyone ever experienced this?

I've noticed that, but not as bad as what you're describing.

My top silencer does thin out quicker that the bottom though....

Any idea why would it do that?

Hitting on the brim of your hat?    

I have noticed it as well with my wool silencers. No idea why though.

My cat wiskers get balled up more on them top and the bottom stays loose all the time.

Split finger.

Mine doen the same!!

My catwiskers also get balled up more on top. I think bonebuster is right about split finger.

Don't notice any wear on my Hush Puppies.        

You might want to video yourself shooting to see what you might be hitting. My old neighbor help start the tranatula's silencers and gave some to me before they hit the market in the late 80's,and haven't worn out yet. Now I don't shoot that bow as much any more but it's lasted for a few strings.