I dont wish to come across in the wrong way, but a good acoustic ear piece if correctly used, (fitted to the ear so the acoustic tube is kept taught from collar clip to ear), you should have no problem with hearing over background noise at high levels (and was designed to deal with such environments). These acoustic ear pieces are designed only to work at their best when tube is kept taught, and if you are using your ear piece correctly and your radio is working correctly then you may need to book yourself in for a hearing test, if im barking up the wrong tree then my apologies and maybe someone else may of learned something lol.
A make i have used for years is the "otto" ear piece, great quality and parts can be removed and easily replaced if damaged. Cost new £40 to £60, as someone mentioned Vestguarduk can supply a similar good quality ear piece for around the same price and are a very good supplier.