audio glitches / pops when using external audio interfaces

This problem seem isolated to my MBP Early 2015 ; Retina 13-inch ; 3.1GHz Core i7 ; 16GB memory ; 512GB SSD ; Intel Iris 6100

I see console messages similar to this one when the glitches, pops occur

HALS_IOContext.cpp:1496:IOWorkLoop_HandleOverload: HALS_IOContext::IOWorkLoop_HandleOverload: Overload on context 256 current time: 15636818 deadline: 15636816

I do not experience the glitches and pops or console messages when using Built-In Output

The pops and glitches do not occur on older MBP models that I own.

I"ve ruled out just about everything but the MBP itself.

The problem occurs using different audio interfaces.

Roland Duo-Capture Ex - USB

Focusrite Clarett 2Pre - Thunderbolt

IconnectMidi2+ - USB

Motu Ultralite Mk3 Hybrid - USB

I have tried every combination of audio bitrate (16 or 24 bit ; 44.1kHz , 48kHz , 96kHz)

I can reproduce with Logic Pro X , MainStage and Reason.

I can reproduce with different IO Buffer Size (64, 128, 256...etc) within the DAW also.

I've reset the PRAM ; reinstalled OS. The problem occurs with El Capitan and Sierra.

Any suggestions or ideas what to look at next ?

thanks

Tim

Austin, Tx