Ash said it was for an "easter egg" they wanted to put on the DVD. I had no idea what that entailed (hey, it was the 1990s), and I asked Ash if I should spend a few hours cleaning up the blocking (I'd slapped it together in less than two hours, which was my free window of time before the next screening). He laughed and said to leave it - the rougher the better. Huh. He left, smiling, and that was the last I thought of it until years later, when someone said to me they laughed at my easter egg. My. Egg... DVD they said... What? They told me it was on the TS2 Supplemental Disc in the Ultimate Toy Box collection. Jessie's Song. That car sequence. Oh. Ah! * yes - a light went on, and Ash's request from years ago came back to me.
By then the interwebs were sophisticated enough that I could search for info about this (this amounts to Googling myself, I suppose)(yoiks)
It turns out the laughs I got by poking fun at the sombre tone in Jessie's abandonment sequence really struck a chord with the directors & producers, so John & Ash requested that this be hidden as an easter egg somewhere in the periphery of the DVDs' Story > Jessie's Song menu, and they layered in some sound f/x. I guess this was picked as an example of the effectiveness of comic relief; we appreciate laughs as much as ever when they are least expected.
Clip from Pixar/Disney. With apologies to Sarah McLachlan, given the perfect tone she struck with her ethereal voice...