Same thing happened to me when I picked up my first USPC. ha ha But seriously don't take it off you will mess it up if you doI just bought the USPc 45 last week and I also own the 45 fullsize. Before I disassembled it I heard rattleing going on inside it and I thought something was broke. I took the slide off and saw the plastic ring and realized it was the buffer. It is very annoying sounding and you would think that HK could have designed it to be more stationary, but there is a reason they made it that way. Do not take it off, it does serve a purpose for the recoil spring.