MacBook Pro Playback distortion

Hello everyone.  I have a computer / server question.  I have an Apple MacBook Pro, 500 GB SSD drive, and 16 gb RAM running under Mojave.  The computer is 98 % used for music, and I placed about 500 CD’s on the drive in AIFF format.  Did this abt 4 months ago, and life has kept me from really listening , until recently. To my surprise , I have a just awful distortion in the playback when using the computer  ??  Low end is actually distorted, and the mids and highs are all off base.  I have took the system down, and worked my way back, starting with just the power amp and an old IPOD Classic ( spinning drive model ) driving the amp directly.  Re-added each part of the system ( with NO, issues ), until I got back to the Apple Computer.  Odd thing is I don’t have the problem when using the computer for on line streaming,  just ITunes when playing back the AIFF copies of the CD’s.


I think I have the I Tunes playback set-up correctly, but maybe not.


Ideas welcome
Used mine that way a lot with no problems. The fact it plays anything back fine streaming or otherwise indicates its not a hardware problem. You're probably right about playback settings. Sounds like a Mac Store or Genius type question.
Try installing BitPerfect on your mac.  Makes a huge difference.  $10
I've never had any problems with playback from my MacBook Air or previous Mac laptops. Which audio output are you using with the MacBook?
I used a mac book pro for years.  I never had noticeable sound problems.    I suspect the distortion could be from the DAC or Preamp or one of the interconnects.  Try another computer source and see if it sounds better.  If so, talk to Apple.  If not re-assess your audio chain.
Thats a sweet machine, one I plan to obtain for myself.  I would:

1) Try a different player. Maybe a free Roon trial.  Will Quicktime play a file?

2) Not sure if Itunes will “see” music on an attached drive. But if Quicktime plays badly from your ssd library, see how it plays from an attached drive. Maybe an issue with the buffers/cache on that local ssd?

3) The mystery is why streamed music plays well but local music doesnt.  Try a rip to Alac just to test. (Though you say the files play well from a iPod Classic. )

Good luck and report back.  
This is the most important part:
Odd thing is I don’t have the problem when using the computer for on line streaming,  just ITunes when playing back the AIFF copies of the CD’s.

If it works for streaming then it can't be hardware. 
Try exporting one of the AIFF files and playing it from another laptop.
Thanks for the replies.  I found the problem to be the Apple I-Tunes settings.  I had the cross fade setting on, and MIDI actualy set for up sampling the playback and did not realize it.  I also added Bit Perfect.  I should had done each thing one by one, but I just changed and added all at one time.  I alos used the Apple power supp;y while playing back.  I was just using the MacBook Pro battery since the cheap wall warts are none for being noisy.  

Play back is fine now.  Thanks to all.

What does your mac pass the signal to? An external DAC? If using an external DAC, how is your mac connected to the DAC? USB cables do make a difference in sound quality. Cheap usb cables will sound like garbage.