Increased engine sound in Toyota Corolla 05

My 2005 Toyota corolla is making more noise in the lower gear for last 2-3K mile. Current millage in the car is 48+K. It sound more like those sports car with high pickup(I guess), specially in the morning (even after warming). As I drive it for few miles the sound reduced.

The dealer suggested to change the drive belt. Any Idea what can be the problem

You need to take it to an independent shop for troubleshooting. The sound may be coming from the exhaust, the engine, or the transmission. I don’t think the dealer is really trying to find the cause of the noise.