Yeah my PS3 is having the same problem it came back from the repair center like that and now I'm annoyed with it all.
The fan sounds like it is going crazy and the machine is louder than ever, if anyone knows what I can do it would be appreciated as I have used up my warranty on repairs on it and I don't feel like it was repaired propperly.
Make sure the system is in a place where it gets enough air flow, first off. You can build a USB fan to increase airflow and place it strategically next to the machine... i've seen this done on youtube videos and it might be worth a try. Depending on your know-how, you can replace your CPU's thermal compound with some AS5 or MX2. Other than that, room temperatures play an obviously large role in this. Hope that helps.