Not just interleaving, but by the look of it also "banding".
DS Actual Rate : 34999000 bps US Actual Rate : 11999000 bps
DS Attainable Rate : 54200248 bps US Attainable Rate : 15545250 bps
Figures ending on 999000 with much higher attainable are the clue.
Lots of noise are generally what causes that.
My broadband basic info/help site - www.robertos.me.uk.
Domains, site and mail hosting - Tsohost
Connection - AAISP Home::1 80/20. Sync 64054/13543Kbps @ 600m. BQMs - IPv4