preemie issues with latching

S • 29. Mama to a rainbow boy. Pregnant with #2.
My son is 2.5 months now (4 weeks adjusted) born at 33w due to IUGR and I've started putting him on the breast more often now that he's gained weight. However, I notice he makes a sound when feeding and it seems like he's not latched properly. I have a very quick letdown and I think it's the problem. Therefore he will latch and unlatch and try to only suck on the nipple. He will feed on both breast for 20 mins total, but will still drink 2 oz right after from the bottle. Any one else dealt with something similar?