I just received a second hand bitmain R4, getting a good hashrate but it's quite loud for an R4 (around 65-70 dB while it's supposed to be 52dB). I've taken it apart removing the fan and when turning it manually i can hear a sort of crunching sound which i'm guessing is metal in the bearings. Only problem is now i'm not sure how to take the fan bearing cover off without breaking it. Has anyone had experience in repairing these or ideas to make it quieter?