perhaps
the record fader (RED) is set higher than the playback fader (GREY)

it is also possible you are hearing two versions of the signal while recording (hence louder) but only one during playback.
I would need to know more about the routing of the signal during record.

Here is an example of my signal routing:
Guitar cab > mic > Mbox > Pro Tools LE

The faders on Pro Tools are always set at 0dB. The thing is that not only do I actually hear it softer during playback, the green meters are also weaker. For example, lets say I check my levels before recording and I decide to keep them at -3dB max. I'll record the track, and then when I play it back, the meters will be lower than -3dB.

If I pan my track hard left or right while I record will it affect the signal?

I don't have a Macintosh and I don't have ProTools but it is possible that the software may reduce all playback levels to prevent overloading the software summing network? Just try mixing your tracks for a final mix and see how it sounds. It could be a feature that's built into the software/hardware combination that many other morons may not have noticed? Certainly not a factor of different analog tape formulations. We're your complaint is a common one.

I am always very PC
Ms. Remy Ann David

There is no fancy software like that on the PT mixer inputs ... just the normal compressor plugs if you choose. I would sugest don't bother while recording .... analog compressing is a different matter and that's cool.

The M-Box does have the balance control ... this can be tricky to understand.
I think it is a blend of direct monitoring and playback monitoring
so during record you hear both what is going to PT and what is coming from PT.
For the track being recorded that is a bit from each and will change on playback only.

M-Box owners please respond and confirm as I don't have one.

I would still like you to check that he red fader during record and the grey fader during playback is at the 0dB nominal position.

Also check that your meters are in the pre fader mode.
I think this is the best way to use the meters.

like kev mentioned:
assuming you have mbox1 not 2 you should set the mix knob all the way to the right for direct monitoring. what your hearing will not be processed by the host comp so it works well for tracking.

try muting the audio track your recording on while tracking.
when you playback it should be the same.