He is, as he sounds, a bit unreliable! (4)
I believe the answer is:
liar
'he is as he sounds a' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'bit unreliable' is the wordplay.
I cannot really see how this works, but
'bit' could be 'i' (resembles 1, a binary digit or bit) and 'i' is found within the answer.
The remaining letters 'lar' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for liar that I've seen before include "not straight [one]" , "Teller of fibs" , "Tale-teller" , "Fabricator" , "Story teller?" .)