My Blower Blows!

So when i got my jeep ('89 Laredo) the blower motor did not work. I swapped in a new one from the junk yard and i noticed that when its off and i flip it on it makes the sound it should when it blows at full force but then it gets quieter and does not blow as hard....is this normal or is something wrong?

-PJ-

Are you sure it's not heater doors opening or closing, changing the force and sound? Blower motor should blow the same all the time unless you have Automatic Temp Control, which I don't think was ever available on XJ.

hmm..maybe thats what im hearing

thanks

-PJ-