Avoid using Trace flags in Startup parameters

Symptoms :
Client did an inplace upgrade from 2000 to 2005 and Server CPU utilization showed quite high during idle times. The CPU utilization is 25% to 29% most of time even there is no user connections to the server.also the SSMS seems to be very slow in response ..

I checked every thing but still could not find any clue ....
I had 2 questions :

1) Why SQL Server is consuming 28-30% CPU when its not doing anything
2) Why everything seems drastically slow at 28% CPU when other instance is pretty fast at 57% CPU .....

I finally checked the Error logs and found that 3 trace flags were enabled in the startup parameter viz. T818,-T815 and -T8809

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