Jeff,
Do you happen to have a Mammoth1 compatible cleaning tape to inspect? If so, please read my thread about cleaning tape ID problems at...
news://{your-nntp-host}:119/ZtCdncngUtn_rFHUnZ2dnUVZ snipped-for-privacy@posted.cpinternet (note: substitute the hated 'aioe.org' for your-nntp-host - works for anyone)
...and let me know what you see in your tape.
Thanks much,
Michael