ALPHABET INC CL C
Alphabet Inc.
Pretty much all of the investing accounts I've had over the last decade have had some kind of garbage in the memo field that I have to clear out. Even when I was downloading Direct Connect from Fidelity they had it, so it doesn't seem to be an Intuit/Quicken thing. I don't think there's anything you can do to stop it, it's already in the data before it arrives at your Mac.
The contents of the Memo field almost always come from your financial institution. You can verify this by clicking on one transaction and pulling down the View menu to select Show Inspector. At the bottom of the Transaction Inpector window, you'llsee the section headed "From your financial institution." In this section, look at the Statement Memo line: this will show exactly what Morgan Stanley downloaded to Quicken. If it shows the memo as you described (e.g. "ALPHABET INC CL C") then Quicken isn't touching what Morgan Stanley provided for download. You'd have to reach out to Morgan Stanley and try to get someone in their external connectivity department to understand the issue and ask them to set the Memo field to blank.
Thanks. I was afraid that's the answer.