The most common and most likely answer to this crossword clue is the 5 letter word THRUM
I've seen this crossword clue in The Times
T
H
R
U
M
More clues leading to the result THRUM
- Loose end left by Bottom, perhaps, in mechanical play
- Continuous murmur from Hard Right splitting corporation
- Drunk hurt before start of military tattoo
- Drone informally during start of meal
- Sound of extraordinary triumph I quietly released
- Buzz Lightyear’s back in hit, briefly
- Cut thread … half of which lost by hesitating?
- Repetitive rhythmic sound from tenor, initially highly strange
- Half of them rumble with a rhythmic sound
- Umpteenth rumba’s to repeat monotonously
Buddy explains!

The straight part
We know that "Loose end/mechanical play" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case loose end/mechanical play = thrum.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does THRUM mean?
THRUM noun- A thrumming sound; a hum or vibration.
- A spicy taste; a tang.
- To cause a steady rhythmic vibration, usually by plucking.
- To make a monotonous drumming noise.
- The ends of the warp threads in a loom which remain unwoven attached to the loom when the web is cut.
- (chiefly in plural) A fringe made of such threads.
- Any short piece of leftover thread or yarn; a tuft or tassel.
- A threadlike part of a flower; a stamen.
- A tuft, bundle, or fringe of any threadlike structures, as hairs on a leaf, fibers of a root.
- A bundle of minute blood vessels, a plexus.
- (chiefly in plural) Small pieces of rope yarn used for making mats or mops.
- A mat made of canvas and tufts of yarn.
- A shove out of place; a small displacement or fault along a seam.
- To furnish with thrums; to insert tufts in; to fringe.
- To insert short pieces of rope-yarn or spun yarn in.
- Made of or woven from thrum.