2000 SAAB 9-3 repair Question ENGINE KNOCKING

Good Evening

I have 111,000 on my saab 93. About two weeks ago, my engine began knocking during early starting. I thought it might be due to the change in temp, but the knocking continue as the car warmed up. I drove the vechicle, the knocking wasn't heard, but wherever I stopped it continued. Upon arriving at work the knocking had stopped and didn't return until two days later, when the knocking returned and hasn't left.

Any thoughts?