Have you actually checked the footage interpretation? Project timebase settings? Sounds like nothing is actualyl wrong, you just don't know AE very well. Dare I say noob alert? Check these settings plus of course the relevant audio preferences and preview settings.
Is this footage variable frame rate? Perhaps Premiere is compensating for the frame rate. You could put the footage in to a timeline in Premiere, tight click on the footage in the timeline and select replace with After Effects composition. Then do what’s needed in AE. Save in AE and the changes would be in Premiere.
Hope this helps.
Oh, the solution was much easier actually! I have checked footage interpretation, it was 30 fps, but there was no way to change it. But then I realised that it must be the default assumption of AE, and it was! I just checked preferences and you can set a frame rate for imported sequence footage. Sorry for the silly question! (yes I AM new to AE))