The reason for asking this question was that you are feeding 20w-50 engine oil which is normally old graded oil. Perhaps your engine doesn’t need it. It needs new grade oil like SM or SN. And when you are feeding it SH, SG, then engine may not feel good for that. Anyway, that was just a possibility.
Some car engines genuinely produce sounds which is little more than normal. Like 1KR-FE, when you drive it over 100 KM/h, the engine sounds become very high. But it comes to normal when reduce the speed. So it maybe the case with 2SZ-FE.
Start engine, open bonnet and push the accelerator. Does it gives the same grinding sound or not ? If no, then chances are that its not engine’s fault.
Sometimes wheel bearings gives the similar sounds when driving. So diagnosing the problem will be 50% solution itself.