Hey just drove home abut 10mins ago. Was coming up to a speedbump in 3rd gear. So i press down on the clutch. Changed to 2nd revs were about 2.5-3k and when my custom exhaust that i got made burble and and had low pop pop pop. Nothing loud just like vrrrmmm..pop..pop..pop and back to normal when driving in 2nd? Will this damage my engine by changing gear down at around 3-4k so it burble and pops ???

I don't think it will affect your engine but you shouldn't downshift like that. iirc if the road speed doesn't match the revs and you change into a lower gear it can wear the clutch down (someone correct me if I'm wrong, I'm no expert).

The engine speed should match the transmission speed (or be higher), you can do this by 'blipping' the accelerator so it revs when the clutch is pressed (only to an rpm that matches the transmission speed). I used to practice this and get as smooth as possible downshift You should also notice a smoother gear change as if you do it without the blip there is usually a sudden pull on the car (engine breaking). It is a racing technique I think, goes with a double de-clutch

As I said I'm not an expert so anyone with more knowledge may correct me.