Good idea for a thread! And surprisingly difficult.
Not sure if it 100% counts because it’s tacked onto the end of the prior track, but the dreadful spoken word “Stockholm Syndrome Interlude” opens up “Stockholm Syndrome” by Blink 182, which is a legitimately good song and one of their best.
The crash-bang-wallop that opens the otherwise superb The Outsiders by Doves. Especially in the context of the album; it jars hard straight after the loveliness that is Kingdom of Rust. No doubt intentional.
Not quite wholly fulfilling the remit but the filthy flute warbling at the start of breathless transforms an average bad seeds song into a less than average one:
In the same way, this great song from Eels has a quite painful start that bothered me a lot in the beginning but I’ve come to love it as part of the song (besides, the harshness and ugliness of it made perfect sense considering what the lyrics are)