Ahh it's probably that they are 48khz .. I don't think PT will import 48khz files into a 44.1khz project. That explains it.
Incidentally, why 48hkz? 44.1hkz is much better suited to use for audio destined for CD or standard web/computer play. 48Khz is specifically for use in video soundtracks (DV/DVD) as it is the native format, where 44.1 is native for most other audio sources.
I know it seems like 48khz will be better han 44.1hkz (more samples per second), but in the end you actually lose potential fidelity because it has to be down sampled to 44.1khz (which doesn't divide nicely from 48khz and introduces the need for the audio engine to
"guess" at some audio frames -- in other words do dithering ... which in turn means it can mangle the actual audio!). In the same vein 88.2Khz is a better choice for higher fidelity recording than 96khz as it down samples evenly (without interpolation or dithering).
Not saying using 48khz is wrong or anything, but just to let you know it introduces much more potential to mangle your audio than using 44.1khz
in the end it's probably splitting hairs (we geeks are all the same) but it can make a big difference for some types of material ... especially when you get into related harmonics and the like ...
Mark