Take it to another mechanic and have it looked out.
If it is a rod knock run it till it dies.
Daily: 1999 328i (202k)- Sport and winter package, 5speed, Jet Black, hellbeige, e60 Short throw, cross drilled rotors, koni, H&R, ASA AR1, Vibrant stealth, basslink
Track: 1995 Mustang GT (230k)- 306ci, 5 speed, MGW shifter, Trickflow Heads, Trickflow intake, street cam, shaved and tucked engine bay, slammed, 1 3/4'' long tubes, tuned with moates.
On the Water: 7' Boneyard Retro Quad Fish