Enquiring Minds...
by Kegler

Thirteen of the clues each contain one incorrect letter.  These incorrect letters, read in clue order,
spell out a phrase related to the title, as described by the phrase in the unclued, shaded entries.
The thirteen correct letters can be anagrammed to spell BY TERRIBLE PUB.

Enquiring Minds grid

Across
9Couples' sound echoes, but not noisily at first (4)
11Shady gold article contains trace of quartz (4)
12Swimmer beginning to taste defeat (5)
13Bottle holds small bit of uranium, detectable with ores (6)
14Studied dynamics inside whirlpool (4)
16Oklahoma city turning back a harlot (5)
18Dane possesses source of unlimited worth (5)
19Feature Bob returning at end of game (4)
21Unruly mob starting to boo bad show (4)
23Yellow bird originally found in most of America (5)
25Horse roaming water's edge (5)
29Cue new diet (4)
31For example, note steamship exit (6)
32Cull away remainder, we hear (5)
33Extraordinary role is temptation (4)
34Blended teas satisfy (4)
Down
1Talent layer distributed at every other position (11)
2Social outcast participating in dinner dance (4)
3Former mate takes too much, grabbing you, finally making departure (6)
4Bureau to start demonstrating vehicles (5)
5Relocate one left out of film (4)
6Mind large treee (4)
7Peer's intrinsic noble quality (5)
8In February, Gore and Unser saw reflecting feature of magician's trunk (5,6)
10First Lady is returning kitchen device (5)
15End of a giant's comment: “Excellent feet” (4)
16Mel's heartless book (4)
17Responses to doctors speak of fantastic locals (3)
20Tie rusts out (5)
22Oregon arrangement creates trauma (6)
24Pack animal in lair, reportedly (5)
26Kind of kook initially has one weakness that's overcome (3-2)
27Meld a group of seven, flipping over the first? (4)
28Performing ant's leader (4)
30I start to see the French key (4)

Solution