Three left I cannot fathom. Suspiciously, they all cross 28a
15d. You are out of tune, I tell you plainly (5,4) T-A-S/-L-T
Something FLAT, I think.
13d In conversation, speak out, beginning to engage one that's near (10). -H-A-S-A-E. CHEAPSKATE fits but makes no sense.
25d. Stumble over, having drunk too much of this (4) -I-S. No idea about this.
Any help gratefully accepted.