Are IR signals affected by nearby atoms?
As was already said,


  IR works on bond lengths. So if the difference is negligible, instrument noise is going to dwarf anything useful you'll pull out.


There will be a difference, and you can definitely detect it computationally, but by normal experimental means (benchtop FT-IR or ATR, not a gas-phase experiment) background noise might the same order of magnitude as any frequency shift you'd see.

For example, the carbonyl stretching frequency and carbonyl bond lengths calculated using B97-D/6-31G(d):

$$
\newcommand{\AA}{\unicode{x212B}}
\begin{array}{llll}
           &amp; \text{bond length} \, (\AA) &amp; \text{frequency, calc.} \, (\text{cm}^{-1}) &amp; \text{frequency, expt.} \, (\text{cm}^{-1}) \\ \hline
\text{pentanal}   &amp; 1.218 &amp; 1772 &amp; 1727 \\
\text{2-hexanone} &amp; 1.223 &amp; 1753 &amp; 1718
\end{array}
$$

Technically, you can distinguish between these in an experiment, but one would be more interested in the presence/absence of a large aldehyde band. This works due to the sharpness of the carbonyl stretch.

Closer to what I think you're asking about is the influence on vibrational frequencies of groups far from the area of substitution. These particular examples are tough because the normal modes of hydrocarbon-like species tend to couple the motion of many $\ce{C-H}$ stretches together. With that in mind, here are the highest-frequency $\ce{C-H}$ stretching modes, which happen to belong to the terminal $\ce{CH3}$ groups. The bond length is for the hydrogen eclipsed with the carbonyl.

$$
\newcommand{\AA}{\unicode{x212B}}
\begin{array}{lll}
           &amp; \text{bond length} \, (\AA) &amp; \text{frequency, calc.} \, (\text{cm}^{-1}) \\ \hline
\text{pentanal}   &amp; 1.102 &amp; 3044 \\
\text{2-hexanone} &amp; 1.102 &amp; 3038
\end{array}
$$

"Wow, that's amazing, you can resolve it!" Not this time. Compare the full spectra for pentanal/valeraldehyde (top) and 2-hexanone (bottom) and try to perform the peak assignment. Is it it the 2960/2962 pair? 2935/2936?




Experimental values/images taken from the Spectral Database for Organic Compounds.