CCCCCTTTTTTTTTTT reads in RNA-seq

Question

[TEman]

I have had some RNA-seq data sets (both single-end and paired-end) with (C)n(T)n sequences.

E.g. 5'-CCCCCTTTTTTTTTTTTTTTTTTTTT-3'

In the paired-end data set, I find this kind of sequence overrepresented in both R1 and R2.

Can someone please enlighten me what this can be?

Thanks