Originally Posted By: B320i
Changed the "mystery" oil in my '93 BMW in 2014 with M1 0w-40. Noise was noticeably worse from the minute I started. The persistent lifter tick was more noticeable, as was VANOS rattle.
Switching to Rotella T6 5w-40 did not cure the problem, but hushed things noticeably. After a while, the car had a change to Penrite HPR10 (10w50, BMW LL-01, ACEA A3/B3, A3/B4 etc), which made things worse again. Its since had a successive change with the Penrite, and the noises do persist. Next OC, will drop to conventional, Shell Helix or GTX 15w-40, and I'll see what happens.
The suspicion I have seen thrown about is that foaming may dampen loud noise to an extent. Castrol is rumoured to foam quite badly, and I've noticed some very light foaming when draining Magnatec 10w30 from a Toyota with a 1GR-FE engine. Apples - Oranges, but when draining the aforementioned M1 after about 12,000km, no foam.
Use a conventional oil to deaden sound. SOPUS works best for me. Doesn't matter if it's Formula Shell, Pennzoil or Quaker State. 10W-30 is fine. No need for 15W-40 diesel oil. Switching from synthetic to conventional means changing more often. But you can still run those mid-grade filters like Fram Tough Guard and Wix for two 5K OCIs (10K).