I'm NOT a CPA, EA, or professional preparer, taking my best stab at this. I'd agree with @Anonymous_ that 1040/2b is the place for this with all your other interest, for reasons posted in more length here:
https://ttlc.intuit.com/community/taxes/discussion/re-i-opened-a-business-bank-account-and-received-...
In short:
- "Disregarded entity," really means "disregarded entity." When the LLC is a single-member LLC being treated as a disregarded entity for personal income tax purposes, file as if the LLC doesn't exist, and you're simply filing as if you're a sole proprietor. In the IRS' eyes, that's exactly what you are.
- Bank interest is not business income. As @Anonymous_ pointed out, it's different from examples "such as notes or accounts receivable" from the Schedule C instructions.
- If you read the instructions related to Schedule C and all other personal income tax forms, the IRS actually doesn't look for your LLC's EIN anywhere related to personal income tax documents including your return! Even if your entity has an EIN, they actually instruct you not to use it, except in a few specific cases.
- The IRS is looking for 1099-INT bank interest income to be reported on Line 1040 / Line 2b. The bank sends your 1099-INT with your EIN on it. The IRS gets it. The IRS sees that the EIN belongs to your SMLLC, and that SMLLC belongs to you, and only you. The IRS will look for the income reported on that 1099-INT, on your 1040/2b (and Schedule B if required). If it's not there, you'll probably get a letter asking why.
